/*
 * SPDX-License-Identifier: Apache-2.0
 *
 * The OpenSearch Contributors require contributions made to
 * this file be licensed under the Apache-2.0 license or a
 * compatible open source license.
 */

/*
 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch licenses this file to you under
 * the Apache License, Version 2.0 (the "License"); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
/*
 * Modifications Copyright OpenSearch Contributors. See
 * GitHub history for details.
 */

package org.opensearch.cluster.metadata;

import com.carrotsearch.hppc.cursors.ObjectCursor;
import org.opensearch.LegacyESVersion;
import org.opensearch.cluster.node.DiscoveryNode;
import org.opensearch.cluster.routing.allocation.RoutingAllocation;
import org.opensearch.cluster.routing.allocation.decider.Decision;
import org.opensearch.common.Booleans;
import org.opensearch.common.settings.Setting;
import org.opensearch.common.settings.Setting.Property;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.OptionalInt;

import static org.opensearch.cluster.metadata.MetadataIndexStateService.isIndexVerifiedBeforeClosed;

/**
 * This class acts as a functional wrapper around the {@code index.auto_expand_replicas} setting.
 * This setting or rather it's value is expanded into a min and max value which requires special handling
 * based on the number of datanodes in the cluster. This class handles all the parsing and streamlines the access to these values.
 *
 * @opensearch.internal
 */
public final class AutoExpandReplicas {
    // the value we recognize in the "max" position to mean all the nodes
    private static final String ALL_NODES_VALUE = "all";

    private static final AutoExpandReplicas FALSE_INSTANCE = new AutoExpandReplicas(0, 0, false);

    public static final Setting<AutoExpandReplicas> SETTING = new Setting<>(
        IndexMetadata.SETTING_AUTO_EXPAND_REPLICAS,
        "false",
        AutoExpandReplicas::parse,
        Property.Dynamic,
        Property.IndexScope
    );

    private static AutoExpandReplicas parse(String value) {
        final int min;
        final int max;
        if (Booleans.isFalse(value)) {
            return FALSE_INSTANCE;
        }
        final int dash = value.indexOf('-');
        if (-1 == dash) {
            throw new IllegalArgumentException(
                "failed to parse [" + IndexMetadata.SETTING_AUTO_EXPAND_REPLICAS + "] from value: [" + value + "] at index " + dash
            );
        }
        final String sMin = value.substring(0, dash);
        try {
            min = Integer.parseInt(sMin);
        } catch (NumberFormatException e) {
            throw new IllegalArgumentException(
                "failed to parse [" + IndexMetadata.SETTING_AUTO_EXPAND_REPLICAS + "] from value: [" + value + "] at index " + dash,
                e
            );
        }
        String sMax = value.substring(dash + 1);
        if (sMax.equals(ALL_NODES_VALUE)) {
            max = Integer.MAX_VALUE;
        } else {
            try {
                max = Integer.parseInt(sMax);
            } catch (NumberFormatException e) {
                throw new IllegalArgumentException(
                    "failed to parse [" + IndexMetadata.SETTING_AUTO_EXPAND_REPLICAS + "] from value: [" + value + "] at index " + dash,
                    e
                );
            }
        }
        return new AutoExpandReplicas(min, max, true);
    }

    private final int minReplicas;
    private final int maxReplicas;
    private final boolean enabled;

    private AutoExpandReplicas(int minReplicas, int maxReplicas, boolean enabled) {
        if (minReplicas > maxReplicas) {
            throw new IllegalArgumentException(
                "["
                    + IndexMetadata.SETTING_AUTO_EXPAND_REPLICAS
                    + "] minReplicas must be =< maxReplicas but wasn't "
                    + minReplicas
                    + " > "
                    + maxReplicas
            );
        }
        this.minReplicas = minReplicas;
        this.maxReplicas = maxReplicas;
        this.enabled = enabled;
    }

    int getMinReplicas() {
        return minReplicas;
    }

    int getMaxReplicas(int numDataNodes) {
        return Math.min(maxReplicas, numDataNodes - 1);
    }

    public int getMaxReplicas() {
        return maxReplicas;
    }

    public boolean isEnabled() {
        return enabled;
    }

    private OptionalInt getDesiredNumberOfReplicas(IndexMetadata indexMetadata, RoutingAllocation allocation) {
        if (enabled) {
            int numMatchingDataNodes = 0;
            // Only start using new logic once all nodes are migrated to 7.6.0, avoiding disruption during an upgrade
            if (allocation.nodes().getMinNodeVersion().onOrAfter(LegacyESVersion.V_7_6_0)) {
                for (ObjectCursor<DiscoveryNode> cursor : allocation.nodes().getDataNodes().values()) {
                    Decision decision = allocation.deciders().shouldAutoExpandToNode(indexMetadata, cursor.value, allocation);
                    if (decision.type() != Decision.Type.NO) {
                        numMatchingDataNodes++;
                    }
                }
            } else {
                numMatchingDataNodes = allocation.nodes().getDataNodes().size();
            }

            final int min = getMinReplicas();
            final int max = getMaxReplicas(numMatchingDataNodes);
            int numberOfReplicas = numMatchingDataNodes - 1;
            if (numberOfReplicas < min) {
                numberOfReplicas = min;
            } else if (numberOfReplicas > max) {
                numberOfReplicas = max;
            }

            if (numberOfReplicas >= min && numberOfReplicas <= max) {
                return OptionalInt.of(numberOfReplicas);
            }
        }
        return OptionalInt.empty();
    }

    @Override
    public String toString() {
        return enabled ? minReplicas + "-" + maxReplicas : "false";
    }

    /**
     * Checks if there are replicas with the auto-expand feature that need to be adapted.
     * Returns a map of updates, which maps the indices to be updated to the desired number of replicas.
     * The map has the desired number of replicas as key and the indices to update as value, as this allows the result
     * of this method to be directly applied to RoutingTable.Builder#updateNumberOfReplicas.
     */
    public static Map<Integer, List<String>> getAutoExpandReplicaChanges(Metadata metadata, RoutingAllocation allocation) {
        Map<Integer, List<String>> nrReplicasChanged = new HashMap<>();

        for (final IndexMetadata indexMetadata : metadata) {
            if (indexMetadata.getState() == IndexMetadata.State.OPEN || isIndexVerifiedBeforeClosed(indexMetadata)) {
                AutoExpandReplicas autoExpandReplicas = SETTING.get(indexMetadata.getSettings());
                autoExpandReplicas.getDesiredNumberOfReplicas(indexMetadata, allocation).ifPresent(numberOfReplicas -> {
                    if (numberOfReplicas != indexMetadata.getNumberOfReplicas()) {
                        nrReplicasChanged.computeIfAbsent(numberOfReplicas, ArrayList::new).add(indexMetadata.getIndex().getName());
                    }
                });
            }
        }
        return nrReplicasChanged;
    }
}
